A compound semiconductor is a compound operating as a semiconductor by combining two or more elements, not a single element such as silicon or germanium. Various kinds of compound semiconductors have been developed and used in various fields. For example, a compound semiconductor may be used for a solar cell and a light emitting element such as a light emitting diode or a laser diode using a photoelectric conversion or a photoelectric conversion element using a Peltier effect.
In particular, the thermoelectric conversion element may be applied for a thermoelectric conversion power generation or a thermoelectric conversion cooling. In general, an N-type thermoelectric semiconductor and a P-type thermoelectric semiconductor are electrically connected in series and thermally connected in parallel. Among them, for the thermoelectric conversion power generation, thermal energy is converted into electric energy by using thermoelectric power generated by applying a temperature difference to the thermoelectric conversion element. In addition, for the thermoelectric conversion cooling, electrical energy is converted into heat energy by utilizing a temperature difference at both ends of the thermoelectric conversion element when DC current flows to both ends of the thermoelectric conversion element.
This thermoelectric technology has an advantage in that heat and electricity may be converted into each other directly and reversibly without using a heat-resistant engine. In particular, as the interest in environment-friendly energy materials has grown recently, the thermoelectric technology is gradually spotlighted as a notable technology.
The energy conversion efficiency of the thermoelectric conversion element is generally dependent on a ZT value which is a performance index of the thermoelectric conversion material. Here, ZT may be determined according to a Seebeck coefficient, electrical conductivity and thermal conductivity, and the higher the ZT value, the better the performance of the thermoelectric conversion material.
Many thermoelectric materials have been proposed and developed for use as thermoelectric conversion elements. Representative groups include chalcogenide series, antimonide series, clathrate series, Half Heusler series, Skutterudite series, and the like.
In the existing technique, the development of thermoelectric materials has been progressing in the direction of improving the characteristics mainly by selecting additives or optimizing the composition, or by implementing a fine lattice utilizing a nanostructure. However, these research directions have a limit in applying the concept of phonon glass and electron crystal, and there are limitations such as lack of reproducibility or difficulty in implementation from an industrial viewpoint.